Question

If a is an obtuse angle in a triangle and sin a = , calculate the exact value of sin 2a.

Answer 1

Explanation:

cos A = √( 1 - (5/13)²) = √( 1 - 25/169) = √(144/169) = - 12 /13

in 2 A = 2 sin A cos A

sin 2 A = 2 *5/13 ( - 12/13 ) = - 120 / 169

the answer is -120/169